This application claims the priority of Japanese Patent Application Nos. 11-75262, 11-75263, filed on Mar. 19, 1999, No. 11-83369 filed on Mar. 26, 1999, which are incorporated herein by reference.
1. Field of the Invention
The present invention relates to an electronic endoscope apparatus and more specifically a configuration of an apparatus which picks up an image of an object to be observed with a solid-state image pickup device by utilizing a magnification changing function to change a viewing distance.
2. Description of the Invention
It has recently been proposed to build a magnification changing drive mechanism for changing a viewing distance, for example, in an insertion tip section of an endoscope and drive a movable lens which is a component member of the magnification changing mechanism. The magnification changing mechanism transmits a rotating drive force of a motor to a magnification changing mechanism section using a linear transmitting member, for example, a multiply coiled spring, which converts a rotating motion into a linear motion to move a predetermined movable lens of an objective optical system frontward and rearward, thereby carrying out a magnification changing operation using a vari-focal optical system for changing a viewing distance or a zoom optical system for changing a focal length. Such a magnification changing drive mechanism allows observance of a magnified image of an object to be observed, thereby :making it possible to perform delicate diagnoses.
However, an electronic endoscope apparatus which has a magnification changing function described above permits magnifying an image of an interior of the object to be observed and allows observance of a detailed image of a focus on a monitor or the like, but on the other hand, it poses a problem that an image to be observed may be blurred. Speaking more concretely, magnification of the image to be observed means magnification of a blur which is caused due to pulsation of a location to be observed or swinging of the tip section of an inserting stage and little in a standard observing condition; and cannot be ignored when a still image is
When the vari-focal optical system is adopted for the magnification changing mechanism to be built in the insertion tip section of an endoscope, it is necessary for focusing after a change of a viewing distance to move the tip section (objective optical system) of the of the endoscope more or less frontward or rearward. Accordingly, an image is liable to be blurred due to the swinging of the tip section as compared with an image in the standard observation mode (without using the magnification changing mechanism).
On the other hand, this kind of endoscope performs automatic light quantity control with a stop mechanism using a stop member or the like to maintain constant image brightness and it is necessary to execute this brightness adjustment in a stable condition even when the magnification changing function described above is used.
Furthermore, a conventional electronic endoscope apparatus has an electronic zoom function to magnify or contract a video signal obtained with a CCD (charge coupled device) which is a solid-state image pickup device. Accordingly, it will be possible to enhance a magnification ratio if this electronic magnification changing function can be combined with an optical magnification changing function described above. In this case, it is demanded not to simply provide the optical magnification changing function and the electronic magnification changing function, but to smoothly switch or change these functions with no strange feeling during a magnification changing operation.
The present invention has been achieved in view of the problem described above and has a primary object to provide an electronic endoscope apparatus which is capable of preventing an image from being blurred when the image is picked up by utilizing a magnification changing mechanism and obtaining stable brightness of the image.
Furthermore, another object of the present invention is to provide an electronic endoscope apparatus which is capable of enhancing a magnification ratio by combining an optical magnification changing function with an electronic magnification changing function and smoothly switching these two functions during a magnification changing operation.
In order to accomplish the objects described above, an electronic endoscope apparatus having a magnification changing function according to a first invention comprises an optical magnification changing mechanism which is capable of optically magnifying an image to be observed with an objective optical system, a solid-state image pickup device which picks up an image of an object to be observed with rays incident from the objective optical system, and an electronic shutter control circuit which controls an electric charge accumulating time of the solid-state image pickup device and sets a high shutter speed to set an exposure time while the magnification changing mechanism is operative which is shorter than that while the magnification changing mechanism is inoperative.
It is preferable for the electronic endoscope apparatus described above to store in a memory various kinds of patterns of electronic shutter speeds which are enhanced as the optical magnification changing mechanism enhances a image magnification ratio and control the electronic shutter speed by reading out data of a pattern selected from the memory.
When an exposure time of approximately {fraction (1/60)} second is set in a standard condition of the configuration according to the first invention, an electronic shutter speed, for example, of {fraction (1/500)} second is set for a magnification at a middle point of the magnification changing operation and an electronic shutter speed of {fraction (1/10000)} second is set for a maximum magnification. That is, a higher shutter speed is set for a higher magnification ratio and the variable setting of the shutter is performed by controlling pulses to discharge electric charges accumulated by a CCD which is a solid-state image pickup device so as to change an electric charge accumulating time left after discharge. When the plurality of patterns of the electronic shutter speeds are stored in the memory, the electronic shutter speeds can be set dependently on magnification ratios, and selected and used dependently on locations to be observed, observing conditions, observer""s demands and so on.
An electronic endoscope apparatus according to a second invention is characterized by comprising not only the optical magnification changing mechanism which optically magnifies an image, the solid-state image pickup device and the electronic shutter control circuit which are described above but also a stop mechanism which variably controls rays output from a light source with a stop member and a control circuit which limits a variable width of the stop mechanism to a predetermined width as the electronic shutter speed is enhanced while the magnification changing mechanism is operative.
The electronic endoscope apparatus described above can comprise a gain control circuit which variably controls a gain of a image signal output from the solid-state image pickup device, thereby being capable of detecting brightness of an image from the video signal with the control circuit and maintaining constant image brightness by controlling the gain of the image signal with the gain control circuit when predetermined brightness cannot be obtained even by the light quantity control with the stop mechanism.
Like the first invention, a configuration, the second invention provides a configuration which varies or controls the shutter speed so as to be higher at a higher magnification ratio by controlling an electric charge accumulating time as a magnification ratio is enhanced. The electronic endoscope apparatus controls the image brightness constant by driving the stop mechanism even during a shutter speed changing operation, but since the shutter speed is set at a high level, the system may allow response of the stop mechanism to be delayed, thereby making the light quantity adjustment unstable and disturbing a screen when the shutter speed is variable within a broad range or when the object to be observed moves abruptly. Therefore, the present invention limits a variable range of the stop mechanism to the predetermined width as the electronic shutter speed is enhanced, thereby preventing the response of the stop mechanism from being delayed and suppressing disturbance of the screen.
On the other hand, a light quantity may be insufficient to obtain definite brightness when the variable amount of the stop mechanism is limited as described above. When brightness is insufficient, the electronic endoscope apparatus according to the second invention therefore controls to enhance the gain of the image signal based on judgement of an image brightness signal such as a luminance signal, thereby maintaining brightness at a constant level by this signal amplification processing.
An electronic endoscope apparatus according to a third invention comprises an optical magnification changing mechanism which is capable of optically magnifying an image to be observed with an objective optical system, a solid-state image pickup device which picks up an image of an object to be observed with rays incident from the objective optical system, an electronic magnification changing circuit which forms a magnified image and contracted image from an image at an operation end of the optical magnification changing mechanism, and a magnification changing speed control circuit which detects a displacement speed of a magnification change in the optical magnification changing mechanism and controls to match this displacement speed with a displacement speed of an electronic magnification change at a switching point between an optical magnification changing operation and an electronic magnification changing operation.
The electronic endoscope apparatus described above is capable of executing the optical magnification changing operation, the electronic magnification changing operation and switching between these operations with a single magnification changing switch.
The configuration according to the third invention is capable of changing a viewing distance from a far position to a near position by driving, for example, a movable lens of the optical magnification changing mechanism and providing an image which is further magnified by operating an electronic magnification changing function after the movable lens reaches the near position. In this case, the electronic endoscope apparatus detects a driven speed of the movable lens, that is, the displacement speed of the magnification change and executes the electronic magnification changing operation at the same displacement speed referring to the displacement speed mentioned above at a stage to shift to the electronic magnification changing operation (also at a stage to return to the optical magnification changing operation). Accordingly, a magnification change of an image can be displayed with no feeling of strangeness even during switching between two functions.
Furthermore, a current electronic shutter speed, a current displacement speed of the optical magnification change and a current optical magnification change or electronic magnification change for an image can be displayed on a monitor.